In photolithography, critical dimension (CD) is the minimum feature size that is to be patterned on the wafer or the minimal distance between adjacent features. The features can be lines but other features can be provided.
Critical dimension scanning electron microscopes (CD-SEM) are used to measure critical dimensions of such features by scanning an area of the wafer that includes such features with an electron beam to provide an SEM image.
A typical CD-SEM is adapted to measure lines or vias. There is a growing need to provide a CD-SEM that can measure other features.